What can affect a player's speed in Halo 3 multiplayer?

Why is it sometimes in Halo 3 multiplayer one character will move slower than the others or two characters will move slower than a third. What things affect speed? Does damage slow you down?

You might be a little more specific as to when exactly you see this speed discrepancy amongst players, but off the top of my head:

• Crouching
• Sprinting
• It's been a while, but I think Power Drain or one of the other consumables has some effect on speed while the players stand in it or walk through it
• Sword lunging
• Being hit by another fast-moving object (i.e. a vehicle)
• Being hit by a concussive force, like a gravity hammer or grenade blast
• Mancannons/grav lifts
• Lag

It is lag if you are playing online, if you are playing custom games on a forge map however, There may be a custom powerup that increases speed or the leader may be set to be slower on the game mode. I believe that is all that can affect speed of one player but not another in Halo 3.